交通荷载对软黏土地区深基坑支挡结构的影响机理及控制机制研究

Combining theoretical analysis, field test, laboratory model test, triaxial test, and numerical analysis method, the mechanism study on the influence and control on retaining structure of deep excavation in soft clay under traffic loading will be studied systematically. The main research contents include: (1) Through theoretical research method, the change regulation of the soil behind a retaining structure under the action of a moving load will be studied. Both the saturated soil and the elastic single-phase soil will be discussed. A rigid retaining structure and a flexible retaining structure will also be discussed. (2) Carry out laboratory model test and field test, the stress path of soil at different locations due to excavation unloading will be studied, and the influence scope and influence range of the traffic loading on the stress in the soil will also be investigated. (3) Considering the change of the stress path caused by excavation unloading and the principal stress axis rotation caused by traffic loading, the dynamic triaxial test of a undisturbed soft clay sample from a deep excavation will be carried out. (4) On the bases of the triaxial test results, by using the numerical analysis method, the influence of the acting position of traffic loading on the bracing structural system will be studied. Besides, many other parameters, such as the amplitude of the loading, the frequency of the loading, and the acting time will also be discussed. In this section, two different models will be considered, those are plane strain model and three-dimensional space model. (5) Carry out the sensitivity analysis of relevant parameters on the dynamic characteristics of the system of the retaining structure of a deep excavation and soft soil. And the influence mechanism will be revealed, the control method will be presented. In general, the successful implementation of present research project will enrich the theory of soil dynamics, and will develop the design theory of deep excavation under the action of traffic loading. Besides, present project will also provide a theoretical basis and technical support for the design, construction and management of a deep excavation.

通过理论研究、现场试验、室内模型试验、三轴试验、数值分析相结合的方法系统研究交通荷载对软黏土地区深基坑支挡结构的影响机理和控制机制。（1）理论研究移动荷载作用下，刚性和弹性支挡结构时、饱和地基和单相地基情况下，地基内应力的变化规律；（2）开展现场试验和室内模型试验，研究开挖卸荷不同位置土体的应力路径，并研究了交通荷载对地基中应力的影响范围和幅度；（3）基于卸荷应力路径和交通荷载引起土体主应力轴旋转，开展软黏土的动三轴试验；（4）利用动三轴试验成果，数值分析研究交通荷载的位置、幅值、频率和作用时间等参数对支挡结构的影响；（5）开展相关参数对交通荷载作用下“深基坑支挡结构-地基”系统动力特性的敏感性分析，揭示出交通荷载对深基坑支挡结构的影响机理，提出相应的控制方法。本项目既能丰富和发展土动力学和交通荷载作用下深基坑的围护设计理论，还可以为深基坑工程的设计、施工和管理提供理论依据和技术支撑。

考虑到邻近交通干道的软土地区深基坑工程数量逐年增加，本项目采用理论研究、现场试验、室内模型试验、三轴试验、数值分析相结合的方法系统研究交通荷载对软黏土地区深基坑支挡结构的影响机理和控制方法。（1）理论研究了桩承式支挡体系的受力问题，给出了桩承式支挡结构中单排桩和双排桩桩身内力和变形的初参数形式解，并发现运用Winkler弹性地基梁理论求解出的桩基托梁最大内力值小于连续梁理论所得结果；（2）通过室内模型试验和数值分析方法对交通荷载作用下悬臂式排桩支挡结构、双排桩支挡结构的受力问题开展研究，发现同等大小的动荷载对围护结构内部弯矩的影响程度要比静荷载大，动荷载对基坑围护结构的影响随着开挖深度的增加而增大，围护结构内部弯矩和侧面土压力的动载系数也随着开挖深度的增加而增大；动荷载的频率对围护结构的受力有一定影响，相同情况下，方波荷载对围护结构的影响大于三角波，三角波荷载的影响大于正弦波；（3）通过开展车辆荷载对软黏土地基内部附加动应力分布影响的现场试验发现，交通动荷载在地基中产生的附加动应力与车速有一定的关系，并且附加动应力随深度衰减，当深度超过一定范围后车辆荷载引起的附加动应力可以不考虑；（4）通过对饱和软黏土的循环扭剪试验发现，相同循环应力比下，随着循环次数的增加，软黏土的应变也在不断增加，主应力轴的连续旋转促使了孔隙水压力的累积，加速了软化，随着循环次数的增加，软土的应力-应变滞回曲线逐渐向轴向应变增大的方向移动；（5）通过开展相关参数对交通荷载作用下深基坑支挡结构的影响分析，编制了考虑交通荷载的基坑围护设计计算程序。本项目研究成果既丰富和发展了土动力学和交通荷载作用下深基坑的围护设计理论，还可以为深基坑工程的设计、施工和管理提供理论依据和技术支撑。